The present invention relates to microlens structures as for example solid immersion lens (SIL) structures and in particular to techniques for constructing SIL structures, as well as selected applications of such structures.
Due to the limitations on resolutions obtainable with conventional optical lenses for applications such as microscopy, techniques have been developed to decrease the Rayleigh limit on transverse resolution δ. The Rayleigh limit is given by δ=0.82λ/(NA) where λ is the wavelength and NA is the numerical aperture of the focusing objective (NA=n sin·(θ)), where n is the refractive index of the medium, and θ is the angle between the outermost rays focusing on the sample and the optical axis)
Coherent light such as laser light can be used to precisely control the wavelength of illumination λ. One way to decrease the transverse resolution is to increase the index of refraction of the optical medium, such as by use of oil-immersion microscopy or use of a solid immersion lens.
If an SIL is placed in contact with the sample under examination, illumination can be more readily focused on it, and use of the high NA of the system allows efficient collection of the excitation light with high optical transmission efficiency and observation of the sample with a very high resolution. In most of the cases, the SIL is used primarily for near-field microscopy, where the air gap between the SIL and the sample oblige those who do not want to use evanescent waves to work with a NA smaller than one.
A problem with the SIL technology is the complexity of its manufacture. For example, a polished glass sphere provided with a sequence of progressively finer alumina powders requires a polishing time typically of many hours. Furthermore, the result is not perfect, and the polished surface is slightly rounded. Moreover, known lens structures in SIL configurations involve objective lens sets that are self contained and thus are difficult to use in a manner that maintains the lens in immersion contact with the object under observation.
What is needed is a method for construction of inexpensive, substantially identical microlenses such as solid immersion lenses and lens elements in arrays and a lens structure which is simple and rapid to construct and which is suited for low-cost, even disposable usage.